The undermanned Celtics had no trouble defeating the Heat 108-89 at TD Garden on Monday night.

Here are 10 takeaways as Boston sits at 17-4 this season after a dominant performance.

1. The defense dominates

The Celtics held the Heat to 34.9 percent from the floor and 20.6 percent from 3-point range.

Every Heat starter shot under 50 percent on the night, as Boston held an opponent under 90 percent for the first time in the regular season since March of last year.

Part of that was because players like Bam Adebayo missed the shots they often took, but the Celtics deserve credit for rotating well, staying out of the way of shooters and consistently forcing the Heat into tough tackles.

2. Cornet above

Luke Kornet was the catalyst on defense, capping his career with six blocks. This time he failed to wag the finger at Dikembe Mutombo, but the Heat certainly got the message.

One of his best blocks came early in the third quarter when he made a last-second assist and blocked Jaime Jaquez Jr.’s shot. The grand finale came moments later when Kornet recovered, denied Tyler Herro and set up a Jayson Tatum 3.

The Celtics are 10-0 when Kornet started over the last two seasons. Coincidence? Probably not.

3. Payton Pritchard is unstoppable

Payton Pritchard contributed 25 points on 10 of 17 shooting, along with five rebounds, four assists, two steals and a block.

According to Celtics statistician Dick Lipe, Pritchard is the first Celtic to have four consecutive 20-point games off the bench since Isaiah Thomas in 2015. He continues to strengthen his position as Sixth Man of the Year and is currently the clear favorite.

He scored at all three levels, was fearless in the lane, and was a pest on defense. And yes, he hit the buzzer again (that was a layup, but it was still impressive).

4. Jaylen Brown lives on the border

Jaylen Brown entered Monday averaging 6.8 free throw attempts per game and shooting at 76.5 percent.

Against the Heat, he increased both stats by attacking the basket early and often and finishing 9 out of 10. Brown is one of the best transition players in the league, so there’s no reason why he shouldn’t get to the line frequently.

When he plays downhill and is confident, he is almost unstoppable.

5. Depth displayed

With Kristaps Porzingis, Jrue Holiday and Al Horford out, Celtics coach Joe Mazzulla used a variety of options.

First up were Derrick White, Brown, Tatum, Jordan Walsh and Kornet. Drew Peterson played 23 minutes, Baylor Scheierman 10 and every Celtic played in some capacity.

Peterson finished the game with 7 points and 7 rebounds and made a conscious effort to work on the glass. Scheierman didn’t take a shot, but was active on defense and made a great no-look pass to Brown at the corner 3.

The reserves have shown that they are ready when they get their chance.

The Heat were without Jimmy Butler, Kevin Love, Nikola Jovic and old friend Josh Richardson. Nobody played particularly well.

6. A bit chaotic in the third part

The win was largely smooth and stress-free for the Celtics, although things got a little sloppy early in the third quarter.

Tatum, who finished with six turnovers, coughed up several times early in the quarter. The Celtics had four turnovers in the first two minutes after only three in the first half.

When they’re at their best, they’re okay with the occasional turnover, just like the top-flight Warriors did a few years ago. As they move the ball with purpose and look for the right shots, occasional misses are inevitable.

But these fluctuations were more likely the result of misunderstandings and apparent complacency, which is not ideal. However, they quickly cleaned it up and got back into shape.

7. An overly confident Derrick White

Derrick White has always been a confident shooter, but right now he looks more confident than ever. White, who shot 5 of 12 from 3 en route to 19 points, wasted no time catching the ball in rhythm.

It doesn’t matter where he is or who is on him. If he has a bit of space, he lets it fly. That’s exactly what he should do. White has made at least four 3-pointers in four straight games and continues to build his All-Star resume.

If he continues like this, he will check his pockets very often.

8. The Peterson Review

After Peterson drained a corner 3, he looked back toward the Heat bench to let them know he meant business.

Peterson, who shined for the Heat in Summer League before his release, reminded his old friends that he was in the lab. He made the most of his opportunity the last two nights and deserves to see time move forward.

9. Dominate the glass

The Celtics recovered quite well, putting up 54 boards to Miami’s 44. Tatum had 11, and Brown, Neemias Queta and Peterson added seven each to lead the way.

Boston isn’t a bad rebounding team (14th entering Monday), but overall it’s definitely an area to strengthen – especially with Porzingis out. This was a promising sign as the Celtics beat their season average by 10.

10. Another quick turnaround

This was the start of a four-game homestand where the Celtics welcome the Pistons to town on Wednesday at 7:30 p.m. After that, it’s the Bucks on Friday, and Marcus Smart returns with the Grizzlies on Saturday.

As of Monday, the Celtics are one game behind the Cavaliers and have the second-best record in the NBA.